A thermally insulating planar component of this type is known commercially as a “vacuum insulation panel”, or “VIP” for short. VIPs are typically used as flat insulating panels in refrigerators or as flat thermal insulation panels for insulating buildings in the construction industry.
Vacuum panels that have highly dispersed ceramic powder enclosed inside an evacuated metal foil envelope enable extremely low thermal conductivity values or heat transfer coefficients with a low structural thickness of only a few millimeters, on the one hand because the metal envelope, which is actually an effective heat conductor, is designed with a very narrow wall thickness of less than 150 μm, and on the other hand because the highly dispersed ceramic powder held between the two planar envelope walls has a very high thermal conductivity resistance or a very low thermal conductivity value, or a very low heat transfer coefficient. This is due, on the one hand, to the inherently low thermal conductivity of ceramic and, on the other hand, to its provision in the form of a highly dispersed powder within an evacuated environment, so that the already inherently low thermal conductivity of ceramic material is further reduced by the conduction of heat beyond particle boundaries, which increases thermal resistance, and by the vacuum conditions present in the spaces between the particles.
“Vacuum” naturally does not refer here to an absolute vacuum, which is not technically feasible in any case, but rather to a gas-poor evacuated state, such as can be produced using prior art means for producing vacuum panels or vacuum insulation panels, in a manner known per se.
VIPs are typically offered in the form of flat panels because this flat panel form is particularly easy and safe to produce. VIPs typically cannot be reshaped into three-dimensionally deformed bodies, since such reshaping would subject at least some areas of the smooth planar envelope walls to intense tensile elongation, usually causing the planar envelope walls made of thin metal foil to crack, even at low degrees of deformation. Even the slightest penetrations or disruptions in the integrity of the planar envelope wall will result in failure of the VIP as a thermally insulating component, first because penetration will destroy the vacuum inside the metal foil envelope, and second because ceramic powder can leak out of the metal foil envelope through the opening produced in the planar envelope wall. The metal foil of the metal foil envelope may be part of a laminate, which may comprise one or more plastic layers in addition to the metal foil. The metal foil may be covered on both sides by at least one plastic film, for the purpose of protection.
The demand for planar thermal insulation components in three-dimensional shapes is increasing in the field of automotive engineering for the purpose of thermally insulating functional spaces in the motor vehicle, such as the engine compartment. Insulating the engine compartment allows the internal combustion engine to cool down more slowly following an operating phase than without insulation, and if it is restarted during a cool-down phase, insulation enables it to heat more quickly to its nominal operating temperature, at which its pollutant emissions correspond to their respective nominal values, which are considerably lower than in a transient cold-start condition.
Planar LWRT components, i.e. porous, compacted thermoplastically bonded fiber material that can be readily reshaped from a fiber mat semifinished product into three-dimensional molded components in press molds with the application of heat, are used for lining engine compartments or more generally for lining functional spaces in motor vehicles.
However, components made from LWRT are beginning to reach their technical limits with the increasing requirements of recent developments in motor vehicles: Varying localized degrees of compaction in the LWRT material result in varying localized thermal conductivity values in the LWRT material in its thickness direction, and thus in varying localized degrees of insulating efficacy. With the increasingly limited space available for accommodating insulating lining components, at least locally higher degrees of compaction of LWRT components are unavoidable in those areas in which very limited space is available at the installation site in the motor vehicle. Other locations where more space is available for accommodating the LWRT material of lining components may be less compacted.
As the compaction of LWRT material increases, its efficacy as a thermal insulator decreases. This is presumably due to the decreasing porosity associated with increasing compaction and to the decreasing thickness of the component—which in this case is desirable.